Existing control systems and control methodologies, particularly those for conveying systems, employ some form of centralized control over multiple device controllers. For example, two device controllers are hard wired interconnected to a programmable logic controller (PLC) or a plurality of PLCs, each being hardwired to device controllers, are hard wired connected to another central PLC. To effect a change in the operation of one device in response to changing conditions for another device, the PLC identifies the changing conditions and sends a signal to the other controller.
Such systems are difficult to modify in the field by the user (i.e, not user friendly). System modifications typically involves re-configuring or replacing each control component (i..e, controller and PLC) in the system. As such, these types of systems are expensive and time consuming and have little flexibility for field modification.
Conveying systems traditionally have been custom designed with centralized controls and complex customized software for tracking articles or goods in movement in the system. Modifications to such systems entail adjustments to the centralized controls, revision to the customized software and the de-bugging required following such changes to assure proper system operation. Further, because the software and controls for each system is customized for each system, it is difficult to combine the control logic with the mechanicals of the conveying system.
There is, therefore, a need for controllers that communicate with each other on a local area basis to control the operation of systems or devices connected to the controllers and need for controllers that de-centralize these control function. Additionally, there is a need for a controllers which do not require hard wired interconnections but use communication protocols and equipment as a means for communicating between controllers. There also is a need for a conveying system that has increased flexibility and controls the flow of goods or articles through the system without centralized control and customized software. Moreover, there is a need for a conveying system that is modularized in design and operation so customized engineering is not required.